Drill strings in earth borehole use are commonly taken apart at threaded connections at ninety-foot, three-joint intervals and usually stand in the derrick as the drill string is removed from the borehole. When the drill string is to be run back into the borehole, the ninety-foot stands are one-by-one attached by threaded connection to the drill string. This is commonly done at intervals to replace dull drill bits or other parts of the downhole assembly.
As drilling proceeds and the hole deepens, the drill string is commonly lengthened by one thirty-foot joint at the time. This joint is normally added to the top end of the string, below the rotational drive device. The rotational drive includes a square or octagonal pipe joint called a Kelly. Each time a single joint of pipe is added to lengthen the drill string, the following sequence takes place: (1) The Kelly is unscrewed from the string; (2) A new joint of drill pipe is positioned and tightened onto the drill string; (3) The Kelly is screwed onto the new joint of drill pipe, and drilling again proceeds. Each threaded drill string tool joint is axially positioned such that the threads to be manipulated are about two feet above the drilling floor before manipulation.
Since the threaded connections of drill string tool joints are tapered somewhat more severely than pipe threads, most of the relative turns between mating threaded elements spin with little torque. The final tightening of a connection or the initial breakout of a connection requires considerable torque. This torque, however, may be required for less than one relative turn of mating connectors. The heavy torque work is commonly done by equipment incapable of rapid spinning of drill pipe.
Historically, the few free turns of threads at each connection have been spun up by a tail chain from a mechanized capstan or "cathead." The tail chain and cathead is a dangerous, time consuming arrangement.
More recently there have been efforts to mechanize the spinning up of the few free turns of the tool joint connection. Spinning devices fall into an all wheel category or into a chain category. This application pertains to the chain type spinner.
Chain type spinners now in use drive the pipe by forcing the chain against the periphery of the pipe in a bight of an incomplete chain loop. The chain is then moved longitudinally in a serpintine, closed path. The chain moves the pipe periphery and hence spins the pipe. This process is best considered with the drawings in hand. At the time of detailed description of drawings herein, a digression will be inserted to differentiate between old and new concepts.